Target says that personal information - including phone numbers, email and mailing addresses - was stolen from as many as 70 million customers in its pre-Christmas data breach, substantially more than the 40 million that the chain had previously said were affected.

The chain also cut its fourth-quarter adjusted earnings forecast and outlook for a key sales barometer.

Target had announced in December that about 40 million credit and debit cards may have been affected by a data breach that happened between November 27 and December 15 - just as the holiday shopping season was getting into gear.

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A Target investigation into the security breach which took place over the busy holiday period showed that the stolen information included names, mailing addresses, phone numbers and email addresses

The retailer said on Friday that the personal information stolen is not a new breach, but was discovered during its ongoing investigation.

Target's shares were down 1.5 percent at $62.40 before the bell on Friday.